MVVM in iOS

Slides from the talk I gave at CocoaHeads Moscow 29.11.13.

Transcript

1. MVVM pattern in iOS development Denis Lebedev, iOS Hipster @ Wargaming ! mailto: d_lebedev@wargaming.net linkedin: http://linkedin.com/in/dlebedev
3. Agenda Wargaming Service Mobile Apps dept. MVC MVVM Development hints Reference
4. WARGAMING SERVICE MOBILE APPS
5. SMA department We make apps for user engagement Quality really matters We experiment a lot with new tools & technologies
6. Apps
7. MODEL-VIEW-CONTROLLER
8. MVC Diagram View Model Controller
9. Classical principles Loose coupling Model is decoupled; view/controller can listen to it’s changes View knows about model, can manipulate controller Controller knows everything and “does all the things” ©
10. View Controller responsibilities Owns & manages view’s state Acts as the datasource for tableviews Maps model’s properties to view values …
11. MASSIVE VIEW CONTROLLER
12. Real world MVC Controllers are ‘almost’ not reusable Controllers are large View is very tight to it’s controller Controllers are hard to unit test
13. Solving Massive Controller problems Separate object acting as tableview dataSource ConverterHelper, ‘MyFancyAttributeToStringHelper’, etc..
14. Testing Unit tests of controllers code is pain Sort of UI tests (Calabash, KIF) is required
15. Wrapping up MVC is not bad at all.
16. Wrapping up What can we do for better world?
17. MODEL-VIEW-VIEWMODEL
18. MVVM Diagram View/ ViewController ViewModel Model
19. MVVM Diagram Wait what? It’s the same!
20. Key differences with MVC ViewController owns it’s view model View model doesn’t know anything about controller
21. Key differences with MVC View/ViewController ViewModel Model ViewController View Model MVC MVVM
22. MVVM Models Can represent single domain entity or collection Responsible for fetching/storing data
23. MVVM Views Cocoa note: MVVM view = view + view controller view is stateless views/view controllers become smaller
24. MVVM View Models encapsulates all view data/properties and binds them to view validation logic actions
25. ReactiveCocoa Functional reactive paradigm in Cocoa world Fancy bindings Composes of sync/async events of any kind Mature, production-ready framework
26. ReactiveCocoa RAC(self, title) = RACObserve(self, viewModel.nickname);
27. ReactiveCocoa RAC(self, stringType) = [RACObserve(self, model.type) map:^id(NSNumber *v) { return v.intValue == 0 ? @"zero" : @"non-zero"; }];
28. Benefits We don’t need to to test the UI (actually we should) We can implement app logic without any UI view model is easy testable view model are (almost) platform independent
29. Platform agnostic code iPad / iPhone / OS X code sharing MVVM + Xamarin = shared Windows / OS X code
30. How we came to MVVM Already familiar with ReactiveCocoa Strong need in good internal testing Fresh project developed from scratch
31. DEVELOPMENT HINTS
32. What actually does view controller? Layout Animations Device rotation View transitions ! All sensible state is stored in view model
33. Instantiation Every controller has viewModel property Some views may have separate view models Inject view model to controller during instantiation Inject view model’s important properties during instantiation
34. ViewModel interface RACSignals as model properties where possible RACSignal for data requests Model property (NSArray, domain object, etc.)
35. WPAFeaturesViewModel.h @interface WPAPlaneFeaturesViewModel : NSObject ! @property (copy, nonatomic) NSArray *planeRows; ! @property (strong, nonatomic, readonly) RACCommand *forwardCommand; @property (strong, nonatomic, readonly) RACSignal *forwardHidden; ! @property (strong, nonatomic) RACSignal *nextPlaneTitle; ! - (instancetype)initWithReferencePlane:(WOWPPlane *)plane classMates:(NSArray *)planes; ! @end
36. ViewModel for tableviews ViewModel has “rows” property of type NSArray Row is some NSObject subclass with data very coupled to cell Formatters, etc. are applied to row class, not cell Controller binds to “rows” and reloads data after property changes
37. WPAPlaneRow.h @interface WPAPlaneRow : NSObject ! @property (strong, nonatomic) WPAFeature *feature; @property (copy, nonatomic) NSString *value; @property (copy, nonatomic) NSString *grade; @property (copy, nonatomic) NSString *referenceGrade; ! @end
38. Testing State of model can be determined in any moment Property change affects view model internal state RACCommand changes view model state RACSignal pushes new state to subscribers ViewModel tests are very obvious and atomic:
39. Real world testing Unit tests for view models Integration tests (for controllers) with KIF
40. IMPERATIVE VS DECLARATIVE
41. How to be functional and reactive Write declarative code instead of imperative Describe how properties are related to each other
42. Functional Reactive view model Almost all code is in constructor Describes how the view should work in terms of commands and properties
43. Functional Reactive view model The login button can be pressed when username and password aren’t blank ! The error should be cleared after 5 seconds it was displayed
44. REFERENCE
45. Functional Reactive view model ReactiveCocoa https://github.com/ReactiveCocoa/ReactiveCocoa ReactiveViewModel https://github.com/ReactiveCocoa/ ReactiveViewModel ! FRP on iOS https://leanpub.com/iosfrp ! FunctionalReactivePixels https://github.com/AshFurrow/ FunctionalReactivePixels MVVMExample https://github.com/garnett/MVVMExample
46. THANK YOU!